TCThe CryosphereTCThe Cryosphere1994-0424Copernicus GmbHGöttingen, Germany10.5194/tc-7-241-2013<i>Brief communication</i> "Important role of the mid-tropospheric atmospheric circulation in the recent surface melt increase over the Greenland ice sheet"FettweisX.1HannaE.2LangC.1BelleflammeA.1ErpicumM.1GalléeH.31Laboratory of Climatology, Department of Geography, University of Liège, n°2 Allé du 6 Aout, 4000, Liège, Belgium2Department of Geography, University of Sheffield, Winter Street, S10 2TN, Sheffield, UK3Laboratoire de Glaciologie et Géophysique de l'Environnement (LGGE), n°54 Rue Moli\`re, 38402, Grenoble, France0702201371241248This work is licensed under a Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/This article is available from http://www.the-cryosphere.net/7/241/2013/tc-7-241-2013.htmlThe full text article is available as a PDF file from http://www.the-cryosphere.net/7/241/2013/tc-7-241-2013.pdf

Since 2007, there has been a series of surface melt records over the
Greenland ice sheet (GrIS), continuing the trend towards increased melt
observed since the end of the 1990's. The last two decades are characterized
by an increase of negative phases of the North Atlantic Oscillation (NAO)
favouring warmer and drier summers than normal over GrIS. In this context, we
use a circulation type classification based on daily 500 hPa geopotential
height to evaluate the role of atmospheric dynamics in this surface melt
acceleration for the last two decades. Due to the lack of direct
observations, the interannual melt variability is gauged here by the summer
(June–July–August) mean temperature from reanalyses at 700 hPa over
Greenland; analogous atmospheric circulations in the past show that
~70% of the 1993–2012 warming at 700 hPa over Greenland has
been driven by changes in the atmospheric flow frequencies. Indeed, the
occurrence of anticyclones centred over the GrIS at the surface and at
500 hPa has doubled since the end of 1990's, which induces more frequent
southerly warm air advection along the western Greenland coast and over the
neighbouring Canadian Arctic Archipelago (CAA). These changes in the NAO
modes explain also why no significant warming has been observed these last
summers over Svalbard, where northerly atmospheric flows are twice as
frequent as before. Therefore, the recent warmer summers over GrIS and CAA
cannot be considered as a long-term climate warming but are more
a consequence of NAO variability affecting atmospheric heat transport.
Although no global model from the CMIP5 database projects subsequent
significant changes in NAO through this century, we cannot exclude the
possibility that the observed NAO changes are due to global warming.